.38 caliber is a frequently used name for the caliber of firearms and firearm cartridges.
The .38 is a large firearm cartridge (anything larger than .32 is considered a large caliber).
[1]: 42 Before 1990, the standard sidearms of police in the United States were revolvers that fired the .38 Special cartridge, seconded by revolvers firing the .357 Magnum, a lengthened version of the .38 Special.
[1]: 68 and all 9mm cartridges